Iron toxicity and other chemical soil constraints to rice in highland swamps of Burundi

Iron toxicity is suspected to be a major nutritional disorder in rice cropping systems established on flooded organic soils that contain reductible iron. A pot trial was carried out to assess Fe toxicity to rice in flooded Burundi highland swamp soils with a wide range of organic carbon contents. Soil and leaf analyses were performed and total grain weight was determined. Clear Fe toxicity was diagnosed, based on leaf Fe content at panicle differentiation. Leaf Fe contents higher than 250 g g^–1 dry matter induced lower Mg (and probably Mn) uptake, and a 50% total grain weight reduction. These features were associated with exchangeable Fe equivalent fractions higher than 86%. Besides, several non-Fe toxic soils exhibited an Mg-Mn imbalance.     

A synthesis of methane emissions from 71 northern,temperate, and subtropical wetlands

Wetlands are the largest natural source of atmospheric methane. Here, we assess controls on methane flux using a database of approximately 19 000 instantaneous measurements from 71 wetland sites located across subtropical, temperate, and northern high latitude regions. Our analyses confirm general controls on wetland methane emissions from soil temperature, water table, and vegetation, but also show that these relationships are modified depending on wetland type (bog, fen, or swamp), region (subarctic to temperate), and disturbance. Fen methane flux was more sensitive to vegetation and less sensitive to temperature than bog or swamp fluxes. The optimal water table for methane flux was consistently below the peat surface in bogs, close to the peat surface in poor fens, and above the peat surface in rich fens. However, the largest flux in bogs occurred when dry 30‐day averaged antecedent conditions were followed by wet conditions, while in fens and swamps, the largest flux occurred when both 30‐day averaged antecedent and current conditions were wet. Drained wetlands exhibited distinct characteristics, e.g. the absence of large flux following wet and warm conditions, suggesting that the same functional relationships between methane flux and environmental conditions cannot be used across pristine and disturbed wetlands. Together, our results suggest that water table and temperature are dominant controls on methane flux in pristine bogs and swamps, while other processes, such as vascular transport in pristine fens, have the potential to partially override the effect of these controls in other wetland types. Because wetland types vary in methane emissions and have distinct controls, these ecosystems need to be considered separately to yield reliable estimates of global wetland methane release.     

火干扰对小兴安岭毛赤杨沼泽温室气体排放动态影响及其影响因素

利用静态箱-气相色谱法,对小兴安岭轻度火烧毛赤杨沼泽CH4、CO2、N2O生长季排放通量进行研究.结果表明:火烧使毛赤杨沼泽生长季CH4排放通量提高485.2％,CO2和N2O排放通量分别下降45.5％、24.8％.火烧未改变CH4季节性排放规律,但改变了CO2、N2O季节性变化规律.火烧样地CH4排放通量与土壤15cm温度间存在显著正相关性关系而与水位相关性不显著,火烧样地CO2排放与土壤0-30 cm温度呈显著或极显著正相关,与水位极显著负相关.对照样地CO2排放通量与土壤0-15 cm温度呈显著或极显著正相关,与水位极显著负相关,火烧使毛赤杨沼泽CH4排放源的强度增强,CO2、N2O的排放消弱,全球温室潜势下降约为43.34％.     

Estimating density of a forest-dwelling bat: a predictive model for Rafinesque’s big-eared bat

Data on species distribution and abundance are the foundation of population ecology. However, due to difficulties in surveying bats, abundance estimates for tree-roosting microchiropterans are non-existent. Therefore, our objective was to develop methods for estimating colony abundance and density, taking as our model Rafinesque’s big-eared bat Corynorhinus rafinesquii, a species of conservation concern found in cypress-gum swamps of the southeastern United States. We searched 123 transects at eight study sites in the Coastal Plain of Georgia, USA to locate and characterize diurnal summer roosts of C. rafinesquii. We modeled the relationship between the number of bat colonies and landscape-scale habitat variables with zero-inflated negative binomial regression and used Akaike’s information criterion to select the most parsimonious models. We generated a predictive density map to identify areas of high colony density and to estimate overall abundance. Colony density was predicted by the duration of wetland flooding, wetland width, and study site. Application of the regression model to a GIS indicated there were 3,734 colonies containing 6,910 adult bats on the eight study sites. Predicted density ranged from 0.07 colonies/ha and 0.07 adult bats/ha in saturated wetlands to 0.47 colonies/ha and 1.18 adult bats/ha in semi-permanently flooded wetlands. This study is the first to estimate density and abundance of forest-dwelling microchiropterans over a large area. Such data can serve as a baseline for future work on population trends in C. rafinesquii. In addition, our approach could be replicated for other bat species with moderately cryptic roosts.     

Biology,natural history and temporal fluctuation of the geometrid Oospila pallidaria associated with host plant phenology

We investigated the temporal fluctuation of the geometrid moth Oospila pallidaria and related it to the leaf flush season of its host plant, Mimosa setosa, and to environmental factors. Aspects of the natural history of adults are also described. Mimosa setosa produced leaves all year round, but abundance of O. pallidaria larvae in the field was seasonal. The abundance of immatures showed a tendency to decrease with rainfall and temperature. Our study is pioneering in that it provides insights into factors related to the occurrence of O. pallidaria in natural areas. In addition, the biology of immatures is provided.     

Structure,function and floristic relationships of plant communities in stressful habitats marginal to the Brazilian Atlantic rainforest

The Brazilian Atlantic rainforest consists of a typical tropical rainforest on mountain slopes, and stands out as a biodiversity hotspot for its high species richness and high level of species endemism. This forest is bordered by plant communities with lower species diversity, due mostly to more extreme environmental conditions than those found in the mesic rainforest. Between the mountain slopes and the sea, the coastal plains have swamp forests, dry semi-deciduous forests and open thicket vegetation on marine sand deposits. At the other extreme, on top of the mountains (>2000 m a.s.l.), the rainforest is substituted by high altitude fields and open thicket vegetation on rocky outcrops. Thus, the plant communities that are marginal to the rainforest are subjected either to flooding, drought, oceanicity or cold winter temperatures. It was found that positive interactions among plants play an important role in the structuring and functioning of a swamp forest, a coastal sandy vegetation and a cold, high altitude vegetation in the state of Rio de Janeiro. Moreover, only a few species seem to adopt this positive role and, therefore, the functioning of these entire systems may rely on them. Curiously, these nurse plants are often epiphytes in the rainforest, and at the study sites are typically terrestrial. Many exhibit crassulacean acid metabolism. Conservation initiatives must treat the Atlantic coastal vegetation as a complex rather than a rainforest alone.     

乐清湾红树林和光滩大型底栖动物群落比较研究

2004年5月,对浙江乐清西门岛的人工红树林及周边滩涂进行大型底栖动物调查,共发现大型底栖动物18种,隶属6门7纲15科;主要是软体动物,节肢动物和环节动物.底上生活类群(groupofsurface,GS)种类数少于底内生活类群(group of surface below,GSB)种类数.通过在红树林、幼红树林和光滩三种生境的调查发现,幼红树林群落结构组成介于红树林和光滩之间,三种生境的大型底栖动物密度分别为452ind·m^-2,310ind·m^-2,620ind·m^-2,生物量分别为40.53g·m^-2,44.80g·m^-2和42.75g·m^-2.红树林区底栖动物的优势种为可口革囊星虫Phascolosoma esculenta和难解不等蛤Enigmonia aenigmatica.三种生境中,红树林的生物多样性和均匀度最高,优势度最小,造成这个现象的原因可能与红树林生境的复杂化有关.     

Social organization and ecology of proboscis monkeys (Nasalis larvatus) in mixed coastal forest in Sarawak

Data are presented from a 16-month study of proboscis monkeys in an area of mixed coastal forest in Sarawak. The population density, social organization, and feeding and ranging behavior are described in detail. Results are compared with those from other primates in an attempt to understand why females of certain species (including proboscis monkeys) transfer between social groups. The scarcity of available food and reasons for the limited habitat preferences of proboscis monkeys are also discussed.     

Ecosystem state shifts during long‐term development of an Amazonian peatland

The most carbon (C)‐dense ecosystems of Amazonia are areas characterized by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here, we present an investigation into long‐term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation ca. 8.9 ka BP), and developed in three stages: (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since ca. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (ca. 6.6–6.1 and ca. 4.9–3.9 ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland–forest swamp–peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on ca. 1.8–1.1 ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.